The central theme of our research efforts continues to be definition of the role of neural and psychologic factors in precipitating sudden cardiac death. The transient risk factor which destabilizes myocardial electrical instability and provokes malignant ventricular arrhythmia appears to reside in the central nervous system. Our focus therefore has been to define the neurophysiologic elements which predispose to ventricular arrhythmias. Laboratory and clinical investigations have concentrated on: 1) further characterization of neural influences on ventricular vulnerability; 2) determining neurochemical correlates of psychologic stress; 3) examination of alterations in central nervous system activity which would protect against ventricular arrhythmias in animals: investigations will explore the effects of central nervous system drugs on cardiac vulnerability. The effects of partial and complete sympathectomy on cardiac vulnerability during psychologic stress will be determined. Mechanisms by which central neurotransmitters affect vulnerability to ventricular fibrillation will be examined. In humans: The major focus will be on recurrent high-grades of arrhythmia. These patients will be clinically, psychiatrically, and psychologically profiled. Biochemical correlates of neural activity during psychologic stress and relaxation response will be examined as related to the occurrence of ventricular ectopic activity.